The present invention relates to a method of manufacturing a ferroelectric layer and a method of manufacturing an electronic instrument.
A ferroelectric such as PZT (Pb(Zr,Ti)O3) has been used for various applications such as a ferroelectric memory, a piezoelectric device, an infrared sensor, and a surface acoustic wave (SAW) device, and has been extensively researched and developed.
As a typical method for forming a ferroelectric, a chemical solution deposition (CSD) method (liquid phase method) such as a sol-gel method or a metalorganic deposition (MOD) method has been known.
The sol-gel method utilizes a solution of a precursor prepared by polymerizing a compound such as a metal alkoxide by hydrolysis and polycondensation (hereinafter may be called “hydrolysis-condensation”). The sol-gel method has an advantage in that a ferroelectric can be obtained with excellent composition controllability by controlling the composition of a metal alkoxide solution. However, since the hydrolysis-condensation reaction is an irreversible reaction, a metal alkoxide which has been crosslinked and polymerized cannot be used as a sol-gel raw material. In particular, when forming a lead-containing ferroelectric such as PZT, it is necessary to process lead waste.
The MOD method utilizes a solution of a stable organometallic compound such as a metal carboxylate. Since the raw material solution used in the MOD method contains a stable organometallic compound as the raw material, it is easy to adjust the solution composition and to handle the raw material solution. On the other hand, since the MOD method forms a complex oxide by decomposing an organic group having a high molecular weight in an oxygen atmosphere, differing from the sol-gel method which forms a complex oxide by hydrolysis and polycondensation of a compound, the crystallization temperature is increased in comparison with the sol-gel method, whereby the crystal grain size tends to be increased.
For example, when connecting a ferroelectric capacitor and a MOS transistor using a tungsten plug, a stacked ferroelectric capacitor having a multilayer structure is used. When forming a ferroelectric layer of the stacked ferroelectric capacitor by the chemical solution method, the following problem occurs. Specifically, a complicated multilayer structure is employed for a lower electrode of the stacked ferroelectric capacitor in order to secure barrier properties for the tungsten plug in the lower layer to prevent oxidation of tungsten. For example, the lower electrode is formed by stacking a nitride layer such as titanium nitride or titanium aluminum nitride, an iridium layer, an iridium oxide layer, and the like on the tungsten plug, and forming a platinum layer on the iridium layer. Since the lower electrode having such a structure cannot allow formation of a platinum layer exhibiting excellent crystal orientation, it is difficult to form a ferroelectric layer exhibiting excellent orientation on the platinum layer when using a known sol-gel method or the like.